US20160243355A1 - Catheters for deploying implantable medical devices, and associated tethering assemblies and methods - Google Patents

Abstract

An operator can release a looped portion of a tethering member, which terminates a distal section thereof, from being secured within a locking lumen of a delivery catheter shaft, and then move the distal section out of engagement with an attachment feature of an implantable medical device to untether the device from the catheter. The tethering member extends within another lumen of the shaft, which may be part of a catheter assembly that further includes a locking member extending within the locking lumen and having a distal tip located in proximity to an aperture of the shaft. To tether the device to the catheter, the operator can engage the tethering member distal section with the device attachment feature, and then pass the looped portion thereof through the aperture and into the locking lumen, where the locking member distal tip can be passed through the looped portion to secure it.

Description

FIELD OF THE DISCLOSURE
• The present disclosure pertains to catheters, and more particularly to catheters for deploying a relatively compact implantable medical device to an implant site, and associated tethering assemblies and methods.
BACKGROUND
• The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical complications and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package for implant in close proximity to the pacing site, for example, within the right ventricle RV of the heart. With reference toFIG. 1, such adevice100 is illustrated, wherein an hermetically sealedenclosure105, preferably formed from a biocompatible and biostable metal such as titanium, contains a pulse generator, or an electronic controller and associated power source (not shown), to which at least oneelectrode111 is coupled, for example, by a hermetic feedthrough assembly (not shown) like those known to those skilled in the.Enclosure105 may be overlaid with an insulative layer, for example, medical grade polyurethane, parylene, or silicone, and a portion of the insulation layer may be removed to formanother electrode112, for example, to provide bipolar pacing and sensing in conjunction withelectrode111.
• FIG. 1 showsdevice100 having been deployed by an operator out from adistal opening203 of adelivery catheter200, which the operator has maneuvered up through the inferior vena cava IVC and the right atrium RA into the right ventricle RV. The deployeddevice100 is shown fixed at an implant site by afixation member115 thereof, but still secured tocatheter200 by atethering member280 that extends out fromdistal opening203 ofcatheter200. Securingdevice100 tocatheter200 withtethering member280 is typically accomplished, prior to maneuveringcatheter200, withdevice100 loaded therein, to the illustrated site, by loopingtethering member280 through anattachment feature121 ofdevice100 and threading first andsecond lengths281,282 oftethering member280 through one or more lumens ofcatheter200 such that opposing ends thereof protrude out from aproximal opening201 ofcatheter200. After deployingdevice100, the operator can grasp the ends oflengths281,282, for example, to tug on tetheringmember280 to test the fixation ofdevice100 at the implant site, and/or to apply a greater force to tetheringmember280 to removedevice100 from the implant site for repositioning at a more suitable site, if necessary. If satisfied with the implant ofdevice100, the operator can remove the loopedtethering member280 from engagement withdevice100 by releasing, for example, the end oflength281, and then pulling on the end of theother length282, thereby withdrawing an entirety oflength282 proximally throughdelivery catheter200 so that theother length281 is pulled distally and through device tether attachment feature121, out from engagement therewith. Such a removal oftethering member280 may tedious, particularly if blood has clotted around tetheringmember280.
SUMMARY
• Embodiments and methods of the present disclosure pertain to improved tethering of relatively compact implantable medical devices in the context of deploying the devices to an implant site via a delivery catheter, for example, to increase the ease of loading the devices into the delivery catheter and/or to increase the ease of untethering, or releasing the devices, after deployment, from securement to the delivery catheter.
• According to some methods, after an operator initially deploys an implantable medical device at an implant site with a delivery catheter to which the device is secured by a distal section of an elongate tethering member, the operator can release a looped portion of the tethering member distal section, which terminates the distal section of the tethering member, from being secured within a locking lumen of a shaft of the catheter, and then pull a proximal section of the tethering member, which protrudes from a proximal end of the catheter, to move the distal section of the tethering member out of engagement with an attachment feature of the device.
• According to some embodiments, the catheter for deploying the device includes an assembly of an elongate shaft, the elongate tethering member, and an elongate locking member, wherein the tethering member extends within a first lumen of the shaft and the locking member within a second (locking) lumen of the shaft. In these embodiments, the locking member includes a distal tip located in proximity to an aperture formed through a sidewall of the shaft, and the tethering member extends from a proximal section thereof to a distal section thereof within the first lumen, wherein the distal section, which is terminated by a looped portion thereof, protrudes from the first lumen at a distal end of the shaft, so that upon engaging the distal section with the attachment feature of the device, the operator can pass the looped portion through the aperture and into the second lumen, and then pass the distal tip of the locking member through the looped portion to secure the looped portion to the catheter shaft and thereby tether the device to the catheter. According to some embodiments, a handle assembly of the catheter includes a button coupled to a proximal end of the locking member for moving the distal tip of the locking member between a first location and a second location, the first location being distal to an entirety of the aperture (i.e., a securing location), and the second location being proximal to a distal edge of the aperture. According to some methods for loading the device into the delivery catheter, after securing the looped portion of the tethering member to the catheter shaft, as described above, the operator can pull the proximal section of the tethering member so that the engaged distal section of the tethering member brings the device into contact with the distal end of the catheter shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
• The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments will hereinafter be described in conjunction with the appended drawings wherein like numerals denote like elements, and:
• FIG. 1 is a schematic showing an exemplary implant of a relatively compact medical device, via an exemplary delivery catheter;
• FIG. 2A is a plan view of a delivery catheter, according to some embodiments;
• FIG. 2B is a plan view of a shaft of the delivery catheter ofFIG. 2A, according to some embodiments;
• FIG. 2C is a cross-section view through section line C-C ofFIG. 2B, according to some embodiments;
• FIG. 2D is an enlarged longitudinal cross-section view of a distal portion of the catheter shaft shown inFIG. 2B, according to some embodiments;
• FIGS. 3A-B are plan views of alternate embodiments of a tethering member that may be employed in the catheter ofFIGS. 2A-D;
• FIG. 4A is a plan view the delivery catheter, according to some embodiments;
• FIG. 4B is an interior plan view of a handle assembly of the delivery catheter, according to some embodiments;
• FIGS. 5A-D are schematics outlining some methods of the present invention; and
• FIGS. 6A-C are schematics outlining some additional methods.
DETAILED DESCRIPTION
• The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives.
• FIG. 2A is a plan view of adelivery catheter300, according to some embodiments.FIG. 2A illustratescatheter300 including ahandle assembly310, an outertubular member320, and aflushing assembly315 coupled to handleassembly310.FIG. 2A further illustrates adistal-most portion322 of outertubular member320 defining adistal opening303 thereof, and, as will be described in greater detail below,distal-most portion322 is sized to contain an implantable medical device for deployment thereof. According to the illustrated embodiment, outertubular member320 is slideably engaged around ashaft420, which is shown in the plan view ofFIG. 2B, separate from a remainder ofcatheter300, and outertubular member320 is coupled to acontrol member311 ofhandle assembly310, which is operable to retract and advancetubular member320 relative toshaft420.FIG. 2B illustratesshaft420 extending from aproximal end421 thereof to distalend422 thereof, whereindistal end422 forms adistal opening402 ofshaft420 and is configured to engage with an implantable medical device (e.g. device100 ofFIG. 1).Delivery catheter300 further includes an optional pull wire assembly, andFIG. 2B shows aproximal end41 of apull wire425 extending out fromshaft420 to be coupled to asecond control member312 ofhandle assembly310, wherein a distal end ofpull wire425 is anchored at alocation42, which is in proximity todistal end422 ofshaft420. According to the illustrated embodiment, movement ofsecond control member312, actuates pullwire425 tobend shaft420 and outertubular member320, for example, to facilitate maneuveringdelivery catheter300 to an implant site.
• FIG. 2B further illustrates aproximal end441 of anelongate locking member440 extending fromproximal end421 ofshaft420. With reference toFIG. 2C, which is a cross-section view through section line C-C ofFIG. 2B, pullwire425 is shown extending within alumen433 ofshaft420, and lockingmember440 is shown extending within anotherlumen432 ofshaft420. According to some embodiments,shaft420 is formed, at least in part, by amulti-lumen tube43, which may be extruded polyether block amide, polyurethane, or silicone rubber, or a composite thereof, and may include an overlay (not shown), for example, formed of braid-reinforced polyether block amide. With further reference toFIG. 2C,multi-lumen tube43 includes the two, relativelysmall lumens432,433, and one, relativelylarge lumen431, wherein lumen341 is in fluid communication withdistal opening402 ofshaft320 and with aproximal port301 of handle assembly310 (FIG. 2A). With reference toFIG. 4B, which will be described in greater detail below,proximal end421 ofshaft420 is shown secured withinhandle assembly310 so thatlumen431 is also in fluid communication with flushingassembly315. According to the illustrated embodiment,lumen431 provides a passageway through which a tethering member, for example, either of the embodiments shown inFIGS. 3A-B, can extend to secure an implantable medical device, such asdevice100, tocatheter300, as described in greater detail below.
• FIG. 2D is an enlarged longitudinal cross-section view of a distal portion ofcatheter shaft420, according to some embodiments, wherein adistal tip442 of lockingmember440 can be seen. With reference back toFIGS. 2B-C, locking member extends fromproximal end441 thereof todistal tip442 thereof withinlumen432 ofshaft440.FIG. 2D illustratesshaft440 including anaperture404 formed through a sidewall thereof in proximity todistal end422, whereinaperture404 provides access tolumen432 and todistal tip442 of lockingmember440 therein.Distal tip442 is shown located proximal to a distal edge ofaperture404, but is moveable withinlumen432 between the illustrated location and another location X, which is distal to an entirety ofaperture404. According to some preferred embodiments,lumen432 is terminated at an end wall in proximity to location X, as shown; alternately,lumen432 extends to, or throughdistal end422. Lockingmember440 may be formed from a relatively rigid metal wire, for example, having a diameter of approximately 0.010 inch. The function of lockingmember440 withincatheter300 is described below in conjunction withFIGS. 5A-C.
• FIGS. 3A-B are plan views of alternative tethering members480-A,480-B, which may be employed bydelivery catheter300.FIG. 3A illustrates tethering member480-A including first andsecond lengths481,482 folded alongside one another so that adistal section82 of tethering member480-A includes a loopedportion820 where first andsecond lengths481,482 meet, and aproximal section81 of tethering member480-A includes terminal ends of eachlength481,482.FIG. 3B illustrates tethering member480-B also including first andsecond lengths481,482, and proximal anddistal sections81,82, but the terminal end ofsecond length482 is joined tofirst length481 alongdistal section82 to form loopedportion820. Each tethering member480-A,480-B may be formed from a polyester fiber having a fluoropolymer coating, such as PTFE. As indicated above, either of tethering members480-A,480-B may extend from the correspondingproximal section81 to the correspondingdistal section82 withinlumen431 of catheter shaft420 (FIG. 2C), andFIG. 4A is a plan view ofdelivery catheter300 in which tethering member480-B is employed as such.FIG. 4A illustratesproximal section481 of tethering member480-B protruding out fromproximal port301 ofhandle assembly310, anddistal section82 of tethering member480-B protruding out fromdistal opening402 ofcatheter shaft420. According to the illustrated embodiment,proximal section81 of tethering member480-B can be clamped withinhandle assembly310 via actuation of aknob586 of avalve member580 that is integrated into a conduit ofhandle assembly310, for example, as shown inFIG. 4B.
• FIG. 4B is a plan view of an internal configuration ofhandle assembly310 wherein a first portion of an outer surface, orshell510A ofhandle assembly310 is removed to see an arrangement of components within a second portion of the shell510B. According to an exemplary embodiment,valve member580 is constructed like a stop-cock valve known to those skilled in the art, and first portion ofshell510A includes anaperture516 formed through a recessedsurface518 thereof, which provides access toknob586 ofvalve member580, so that an operator can rotateknob586 between an open position and a closed position, per arrow C. The open position allows free movement of tethering member480-B withinshaft420, while the closed position clamps down onproximal section81 of tethering member480-B.FIG. 4B illustrates abutton540 located in proximity toproximal end421 ofcatheter shaft420 and acorresponding aperture514 formed through first portion ofshell510A to provide the operator access tobutton540. With reference back toFIG. 2B, according to some embodiments,button540 is coupled toproximal end441 of lockingmember440, so that the operator can movedistal tip442 of lockingmember440 between the above-described locations, relative to aperture404 (FIG. 2D), by movingbutton540 proximally and distally, per arrow M.FIG. 4B further illustrates anoptional detent feature504 formed along an edge ofaperture514 to engage a neck ofbutton540 and thereby provide some resistance to accidentally movingbutton540 proximally from a distal location that positions locking memberdistal tip442 distal to an entirety ofaperture404, for example, at location X. Alternately a safety catch or toggle member may be integrated intohandle assembly310 to prevent accidental movement ofbutton540 from the distal location.
• With further reference toFIG. 4A, outertubular member320 is shown having been retracted relative toshaft420, for example, by movingcontrol member311 proximally, per arrow R, so thataperture404 ofshaft420 is exposed distal todistal-most portion322 of outertubular member320. Withdelivery catheter300 in this illustrated configuration, a relatively compact implantable medical device (e.g., device100) can be loaded therein, for example, according to methods outlined in conjunction withFIGS. 5A-D.
• FIG. 5A showsdistal section82 of tethering member480-B having been engaged withattachment feature121 ofdevice100, for example, by threadingdistal section82 through an opening thereof.FIG. 5A further illustrates loopedportion820 of the engageddistal section82 being pulled proximally, per arrow P1, towardaperture404 ofcatheter shaft420, whiledistal tip442 of lockingmember440, withinlumen432, is located proximal to the distal edge ofaperture404. InFIG. 5B, the operator has passed loopedportion820 of tethering member480-B throughaperture404 and intolumen432 so thatdistal tip442 of lockingmember440 can be passed through loopedportion820 and moved, per arrow M-S, into location X, distal to an entirety toaperture404, for example, as shown with a dashed line inFIG. 5C.
• With further reference toFIG. 5B, after movingdistal tip442, per arrow M-S, the operator can pullproximal section81 of tethering member480-B (FIG. 4A) to bringdevice100 into contact withdistal end422 ofcatheter shaft440, per arrow P2, and then, according to some methods, rotateknob586 of valve member580 (FIG. 4B) to clamp down onproximal section81 inhandle assembly310, and thereby secureproximal section81 to the proximal end ofcatheter300. With further reference toFIG. 5C, after bringingdevice100 into contact withdistal end422 ofcatheter shaft420, the operator can advance outertubular member320, per arrow A, over shaftdistal end422 anddevice100, for example, as shown inFIG. 5D.
• The figures illustratedistal end422 ofcatheter shaft420 being enlarged from a remainder ofshaft420 to encloseattachment feature121 and generally conform to a proximal end ofdevice100, according to some embodiments. In these embodiments,distal end422 may include apassageway428 formed therein, for example, a groove, as seen in the cross-section view ofFIG. 2C, or a hole as seen inFIG. 2D.Passageway428 can receive insertion ofdistal section82 of tethering member480-B therethrough, after the operator engagesdistal section82 withattachment feature121, for example, when the operator passes loopedportion820 throughaperture404 and intolumen432 ofshaft440. According to some alternate embodiments,distal end422 ofshaft420 need not be enlarged and need not includepassageway428.
• With further reference toFIG. 5D, an interior ofdistal-most portion322 of outertubular member320 is shown being sized to containdevice100 and shaftdistal end422 in contact therewith. According to the illustrated embodiment, advancing outertubular member320 overdevice100 moves a plurality of fixation fingers offixation member115 from a relaxed condition (FIGS. 5A-C) to an extended condition shown inFIG. 5D.Fixation member115 may be cut from Nitinol tubing, according to methods known in the art, and the super-elastic nature of Nitinol allows the fingers thereof to elastically deform between the relaxed and extended conditions. The extended condition of the fixation fingers allows for initial engagement thereof with tissue, whencatheter300 is employed to deploydevice100 at an implant site, for example, according to some methods described in conjunction with the schematics ofFIG. 1 andFIGS. 6A-C.
• Catheter300, afterdevice100 is loaded therein, may be advanced by the operator into a body of a patient and maneuvered into proximity with an implant site. With reference back toFIG. 1,catheter300, likecatheter200, can be maneuvered up through the inferior vena cava IVC and into the right ventricle RV, from the right atrium RA, to approach an implant site.FIG. 6A shows fingers of device fixation member150 initially engaging tissue T at the implant site as outertubular member320 of catheter is retracted, per arrow R. When fixation member150 ofdevice100 is fully engaged with tissue T, as seen inFIG. 6B,delivery catheter300 can be withdrawn, per arrow W. If the operator previously clamped down onproximal section81 of tethering member480-B, when loadingdevice100 intocatheter300, by rotatingknob586 to closevalve member580 of handle assembly310 (FIG. 4B), the operator now rotatesknob586 in an opposite direction to openvalve member580, thereby allowing free movement of tethering member480-B withinshaft420 while withdrawingcatheter300. According to some methods, after openingvalve member580, the operator may tug onproximal section81 of tethering member480-B to test the fixation ofdevice100 at the implant site, and then, if fixation is adequate, proceed to withdrawcatheter300 away fromdevice100.
• With further reference toFIG. 6B, becausedistal section82 of tethering member480-B is still secured to catheter300 (by lockingmember440 in lumen432), the withdrawal ofcatheter300 pulls tethering member480-B through the opening ofdevice attachment feature121, per arrow S. But, with reference toFIG. 6C, a length ofproximal section81 of tethering member480-B is long enough to still protrude fromproximal port301 ofcatheter300, so that the operator can maintain control over the tethering ofdevice100 tocatheter300, until the operator determines thatdevice100 can be untethered fromcatheter300.FIG. 6C showsdevice100 fixed to tissue T at the implant site and still tethered, but withcatheter300 withdrawn a distance fromdevice100 so that the operator can evaluate the performance ofdevice100, for example, pacing and sensing, without mechanical interference fromcatheter300. If the operator finds the performance ofdevice100 satisfactory,device100 can be untethered andcatheter300 completely withdrawn from the body of the patient. According to some methods foruntethering device100, the operator releases loopedportion820 ofdistal section82 of tethering member480-B from being secured in lumen432 (FIG. 5C), by movingdistal tip442 of lockingmember440 per arrow M-R ofFIG. 5B, which may be accomplished via button540 (FIG. 4B), and then by pullingproximal section81 of tethering member480-B to disengagedistal section82 from attachment feature121 ofdevice100, per arrow U ofFIG. 5A.
• In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.

Claims (20)

1. A method for loading a relatively compact implantable medical device into a delivery catheter, the method comprising:

engaging a distal section of a tethering member with an attachment feature of the implantable medical device, the tethering member extending from a proximal section thereof to the distal section thereof within a first lumen of a shaft of the catheter, the proximal section protruding from a proximal end of the catheter, and the distal section protruding from a distal end of the shaft;

passing a looped portion of the engaged distal section of the tethering member into a second lumen of the catheter shaft, through an aperture in a sidewall of the shaft, the aperture being located in proximity to, and proximal to the distal end of the shaft;

passing a distal tip of an elongate locking member through the looped portion of the engaged distal section of the tethering member, after passing the looped portion through the aperture, the locking member extending within the second lumen of the catheter;

moving the distal tip of the locking member into a location distal to the aperture, after passing the distal tip through the looped portion of the engaged distal section of the tethering member, to secure the looped portion to the catheter shaft; and

pulling the proximal section of the tethering member so that the engaged distal section of the tethering member brings the device into contact with the distal end of the catheter shaft, after moving the distal tip of the locking member into the location distal to the aperture.

2. The method ofclaim 1, further comprising securing the proximal section of the tether member to the proximal end of the catheter, after pulling the proximal section of the tethering member to bring the device into contact with the distal end of the catheter shaft.

3. The method ofclaim 1, further comprising advancing an outer tubular member of the catheter over the device, after bringing the device into contact with the distal end of the catheter shaft by pulling the proximal section of the tethering member, the outer tubular member being slideably engaged around the shaft.

4. The method ofclaim 1, further comprising inserting a segment of the distal section of the tethering member through a passageway formed in the distal end of the catheter shaft, after engaging the distal section with the attachment feature of the device.

5. A delivery catheter for deploying a relatively compact implantable medical device to an implant site, the catheter comprising:

an elongate shaft extending from a proximal end thereof to a distal end thereof, the shaft including a first lumen, a second lumen, and an aperture formed through a sidewall of the shaft and being located in proximity to, and proximal to the distal end of the shaft, the aperture providing access to the second lumen through the sidewall;

an elongate tethering member extending from a proximal section thereof to a distal section thereof within the first lumen of the shaft, the distal section protruding from the first lumen at the distal end of the shaft, being configured for engaging with an attachment feature of the implantable medical device, and including a looped portion that terminates the distal section, and the aperture of the shaft being sized to allow passage of the looped portion therethrough and into the second lumen of the shaft; and

an elongate locking member extending from a proximal end thereof to a distal tip thereof within the second lumen of the shaft, the distal tip being located in proximity to the aperture of the shaft, and the distal tip being configured to pass through the looped portion of the distal section of the tethering member; and

a handle assembly coupled to the proximal end of the shaft, the proximal section of the tethering member protruding from the handle assembly, the handle assembly including a button coupled to the proximal end of the locking member for moving the distal tip of the locking member between a first location and a second location, the first location being distal to and entirety of the aperture, and the second location being proximal to a distal edge of the aperture.

6. The catheter ofclaim 5, wherein the distal end of the shaft is enlarged from a remainder of the shaft, being configured to generally conform to a proximal end of the implantable medical device.

7. The catheter ofclaim 6, the distal end of the shaft includes a passageway formed therein, the passageway configured to receive the distal section of the tethering member, when the looped portion thereof is passed through the aperture and into the second lumen of the shaft.

8. The catheter ofclaim 5, further comprising:

a pull wire assembly including an elongate pull wire and an anchor band, the pull wire extending from a proximal end thereof to a distal end thereof, and the anchor band being mounted to the shaft and coupled to the distal end of the pull wire; and

wherein the shaft further includes a third lumen in which the pull wire extends; and

the handle assembly further includes a control member coupled to the proximal end of the pull wire.

9. The catheter ofclaim 5, wherein the handle assembly further includes a clamping subassembly, the clamping subassembly being operable to secure the proximal section of the tethering member within the handle assembly.

10. The catheter ofclaim 5, further comprising an elongate outer tubular member slideably engaged around the shaft, the outer tubular member including a distal-most portion sized to contain the medical device and the distal end of the shaft therein, when the medical device is in contact with the distal end of the shaft.

11. An assembly for a delivery catheter, the catheter for deploying a relatively compact implantable medical device to an implant site, and the assembly comprising:

an elongate shaft extending from a proximal end thereof to a distal end thereof, the shaft including a first lumen, a second lumen, and an aperture formed through a sidewall of the shaft and being located in proximity to, and proximal to the distal end of the shaft, the aperture providing access to the second lumen through the sidewall;

an elongate tethering member extending from a proximal section thereof to a distal section thereof within the first lumen of the shaft, the proximal section protruding from the first lumen at the proximal end of the shaft, the distal section protruding from the first lumen at the distal end of the shaft, being configured for engaging with an attachment feature of the implantable medical device, and including a looped portion that terminates the distal section, and the aperture of the shaft being sized to allow passage of the looped portion therethrough and into the second lumen of the shaft; and

an elongate locking member extending from a proximal end thereof to a distal tip thereof within the second lumen of the shaft, the distal tip being configured to pass through the looped portion of the distal section of the tethering member, and the distal tip being moveable with the second lumen between a first location and a second location, the first location being distal to an entirety of the aperture, and the second location being proximal to a distal edge of the aperture.

12. The assembly ofclaim 11, wherein the distal end of the shaft is enlarged from a remainder of the shaft, being configured to generally conform to a proximal end of the implantable medical device.

13. The assembly ofclaim 12, the distal end of the shaft includes a passageway formed therein, the passageway configured to receive the distal section of the tethering member, when the looped portion thereof is passed through the aperture and into the second lumen of the shaft.

14. The assembly ofclaim 11, wherein the shaft further includes a third lumen and a pull wire sub-assembly, the pull wire sub-assembly including an elongate pull wire, and an anchor band, the pull wire extending within the third lumen, from a proximal end thereof to a distal end thereof, and the pull band being mounted to the shaft and coupled to the distal end of the pull wire.

15. A method for deploying a relatively compact implantable medical device to an implant site, the method comprising:

loading the device into a delivery catheter such that a proximal end of the device is engaged with a distal end of a shaft of the catheter and a distal-most portion of outer tubular member of the catheter contains the device;

advancing the catheter with the device loaded therein into a body of a patient;

maneuvering the distal-most portion of the advanced catheter into proximity with the implant site;

retracting the outer tubular member of the catheter with respect to the catheter shaft to expose the device for engagement with tissue at the implant site, the outer tubular member being slideably engaged around the catheter shaft;

releasing a looped portion of a distal section of a tethering member from being secured within a locking lumen of the catheter shaft, the looped portion terminating the distal section, the distal section being engaged with an attachment feature of the device, the tethering member extending from the distal section to a proximal section thereof within another lumen of the catheter shaft; and

pulling the proximal section of the tethering member to move the distal section of the tethering member out of engagement with the attachment feature of the device, after releasing the looped portion of the distal section.

16. The method ofclaim 15, wherein loading the device into the delivery catheter comprises:

engaging the distal section of the tethering member with the attachment feature of the implantable medical device;

passing the looped portion of the engaged distal section of the tethering member into the locking lumen of the catheter shaft, through an aperture in a sidewall of the shaft, the aperture being located in proximity to, and proximal to the distal end of the shaft;

passing a distal tip of an elongate locking member through the looped portion of the engaged distal section of the tethering member, after passing the looped portion through the aperture, the locking member extending within the locking lumen of the catheter;

moving the distal tip of the locking member into a location distal to the aperture, after passing the distal tip through the looped portion of the engaged distal section of the tethering member, to secure the looped portion within the locking lumen of the catheter shaft; and

pulling the proximal section of the tethering member so that the engaged distal section of the tethering member brings the device into contact with the distal end of the catheter shaft, after moving the distal tip of the locking member into the location distal to the aperture.

17. The method ofclaim 16, wherein loading the device further comprises securing the proximal section of the tether member to a proximal end of the catheter, after pulling the proximal section of the tethering member to bring the device into contact with the distal end of the catheter shaft.

18. The method ofclaim 16, wherein loading the device further comprises advancing the outer tubular member of the catheter over the device, after bringing the device into contact with the distal end of the catheter shaft by pulling the proximal section of the tethering member.

19. The method ofclaim 16, wherein loading the device further comprises inserting a segment of the distal section of the tethering member into a passageway formed in the distal end of the catheter shaft, after engaging the distal section with the attachment feature of the device.

20. The method ofclaim 15, wherein releasing the looped portion of the distal section of the tether member from being secured within the locking lumen comprises moving a distal tip of an elongate locking member proximally, from a first location to a second location, the first location being distal to an aperture formed through a sidewall of the catheter shaft, the second location being proximal to a distal edge of the aperture, and the aperture being located in proximity to, and proximal to the distal end of the catheter shaft and providing access to the locking lumen through the sidewall.

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